In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are now also starting to be introduced in mass production. Further, research is also being conducted into lithography techniques that use F2 excimer lasers, electron beam, extreme ultraviolet radiation (EUV), X ray and the like as the light source (radiation source).
One example of a known resist that is capable of producing patterns of minute dimensions is a chemically amplified resist, which includes a base resin capable of forming a film and an acid generator that generates acid upon exposure. These chemically amplified resists include negative resists in which the alkali solubility of the exposed portions decreases, and positive resists in which the alkali solubility of the exposed portions increases.
Conventionally, polyhydroxystyrene (PHS) or derivative resins thereof in which the hydroxyl groups have been protected with acid-dissociable, dissolution-inhibiting groups (PHS-based resins), and copolymers derived from (meth)acrylate ester or derivative resins thereof in which the carboxyl groups have been protected with acid dissociable, dissolution inhibiting groups, have been used as the base resin component of chemically amplified resists.
However, when a pattern is formed using this type of pattern-forming material, a problem arises in that roughness may develop on the upper surface and side wall surfaces of the pattern. For example, the roughness on the side wall surfaces of the resist pattern called line edge roughness (LER) causes distortion around the periphery of the holes of a hole pattern and fluctuation of line width of a line and space pattern. As a result, adverse effects may be caused in the production of fine semiconductor devices.
This problem of surface roughness becomes more serious as the pattern size becomes smaller. Therefore, for example, in lithography using electron beam or EUV, very fine patterns of a few 10 nm is a goal, which means that an extremely low pattern roughness beyond the present pattern roughness is desired.
However, a polymer typically used as the base component has a molecular size (mean square radius of a molecule) as large as about a few nanometers. In the developing process of pattern formation, the resist generally exhibits a dissolution behavior corresponding to one molecule of the base component. For this reason, as long as such a polymer is used as the base component, it is extremely difficult to further reduce the roughness.
For solving the above-mentioned problems, resists using a low molecular weight material as the base component have been proposed as a material for achieving extremely low roughness. For example, in Patent Documents 1 and 2, there has been proposed a low molecular weight material having alkali soluble groups such as hydroxyl groups in which some or all of the alkali soluble groups are protected with acid dissociable, dissolution inhibiting groups. Such a low molecular weight material has a small molecular size as it has a low molecular weight, and hence, it is expected to be capable of reducing the roughness.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2002-099088
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2002-099089